I am developing a frame-based simulation that uses a viterbi decoder. I found that the vitdec function takes tblen as a parameter and I didn't know what to put as a best value for this parameter. I noticed that changing the value of this parameter will affect the result BER curve, in other words, I got different SNRs for BER = 1e-3. Is this logical and what is the best value for tblen?

C?sar Ghali wrote:
> Dear friends,
>
> I am developing a frame-based simulation that uses a viterbi decoder. I found that the vitdec function takes tblen as a parameter and I didn't know what to put as a best value for this parameter. I noticed that changing the value of this parameter will affect the result BER curve, in other words, I got different SNRs for BER = 1e-3. Is this logical and what is the best value for tblen?
>
> Thanks in advance for your help.
>
>
> Cesar Ghali

That's the traceback depth of your Viterbi algorithm. There is no exact
theoretical answer to this question. Clearly, the longer the traceback
depth, the better performance you will get, but then the VA needs more
memory and will add more latency to your system.
The rough rule of thumb for traceback depth is 5-7 times the constraint
length of the code. The idea is that at that depth all your surviving
paths will have merged (in most cases), so there isn't much to be gained
by setting the traceback depth longer that this. You can experimentally
determine the best value for your particular code and application.

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